The invention relates to a method of testing a modified Booth multiplier for multiplying an m-bit value .vertline.X=x(m-1) . . . x(1) x(0), where x(0) is the least-significant bit.vertline., by an n-bit value .vertline.Y=y(n-1) . . . y(1) y(0), where y(0) is the least-significant bit.vertline.. The modified Booth multiplier comprises a Booth encoder in which the n-bit value is converted into a series of multiplication values (Y'=y'(k-2) . . . y'(2) y'(0), where k=n if n is even and k=n+1 if n is odd. The conversion occurs in groups of 3 bits, which overlap each time by one bit. The groups of 3 bits take the form y(i-1) y(i) y(i+1), where i=0, 2, 4, . . . n-1 if n is even and i=0, 2, 4, . . . n-1 if n is odd. The bits y(-1) and, if n is odd, and y(n) have adjustable values. The modified booth multiplier further comprises a multiplex circuit for forming partial products (X.y'(j)), and a matrix configuration of full adders for adding the successively obtained partial products in incremental positions. According to the method a number of test patterns is obtained in the modified Booth multiplier on the basis of specifically applied X,Y values. The test patterns produce values, on an output of the modified Booth multiplier, that reveal whether the modified Booth multiplier is defective.
The design of a modified Booth multiplier should be aimed not only at realizing specific functions in a given structure, but also at taking into account the testability of the modified Booth multiplier. The hardware of the modified Booth multiplier should be such that its constituent components and its operation can be simply tested. It is always possible, that is to say without taking specific steps, to generate a variety of series of test patterns for supply to the modified Booth multiplier and to test an output thereof as regards the values associated with the relevant test pattern. For a modified Booth multiplier for a substantial number of bits to be processed, the number of feasible test patterns is so large that this method of testing is not very efficient and often even impracticable.